Method to make fiber/polymer composite with nonuniformly distributed polymer matrix

ABSTRACT

A method of making a composite of a unidirectional fibrous web in a polymer matrix composition by nonuniformly feeding a polymer composition into contact with a unidirectional fibrous web into a gap between two adjacent compression surfaces with at least one of the surfaces having a pattern. This results in the polymer becoming nonuniformly distributed into thick areas and thin areas as a matrix for the fibrous web.

BACKGROUND OF THE INVENTION

Ballistic article such as bulletproof vests, helmets, armor plate andother military equipment, structural members of helicopters, aircraft,ships, and vehicle panels and briefcases containing high strength fibersare known. Fibers conventionally used include aramid fibers, fibers suchas poly(phenylenediamine terephthalamide), graphite fibers, ceramicfibers, nylon fibers, glass fibers and the like. For these applications,the fibers are ordinarily encapsulated or embedded in a rigid matrixmaterial and, in some instances, are joined with rigid facing layers toform complex composite structures.

U.S. Pat. Nos. 4,403,012: 4,457,985 4,501,856: 4,543,286 4,623,574:4,650,710 disclose ballistic resistant composite article comprised ofnetworks of high strength fibers in matrices composed of olefin polymersand copolymers, unsaturated polyester resins, epoxy resins, and otherresins curable below the melting point of the fiber. While suchcomposites provide effective ballistic resistance, A. L. Lastnik, et al."The Effect of Resin Concentration and Laminating Pressures on KevlarFabric Bonded with Modified Phenolic Resin", Technical ReportNATICK/TR-84/030, June 8, 1984, have disclosed that an interstitialresin, which encapsulates and bonds the fibers of a fabric, reduces theballistic resistance of the resultant composite article. Therefore, aneed exists to improve the structure of composites to effectivelyutilize the properties of the high strength fibers.

U.S. Pat. No. 4,623,514, Harpell et al., filed Jan. 14, 1985, andcommonly assigned, discloses a simple composites..comprising highstrength fibers embedded in an elastomeric matrix. Surprisingly, thesimple composite structure exhibits outstanding ballistic protection ascompared to simple composite utilizing rigid matrices, the results ofwhich are disclosed therein. Particularly effective are simplecomposites employing ultra-high molecular weight polyethylene andpolypropylene such as disclosed in U.S. Pat. No. 4,413,110.

A limitation of the composites disclosed in the art is that thepercentage of resin is at least 10 volume percent. U.S. Pat. No.4,650,710 discloses that the fiber network comprises at least 50 volumepercent of the fabric layer, more preferably at least about 70 volumepercent, and most preferably at least about 90 volume percent. Thispatent notes that the volume percent of elastomer in a fabric layer ispreferably less than 15 volume percent, more preferably less than about10 volume percent, and most preferably less than about 5 volume percent.It is desirable to maintain as high a volume percent of fabric aspossible to enhance ballistic resistance.

However, patents such as U.S. Pat. No. 4,623,574 show the difficulty inpreparing a composite made of a fabric web within a polymeric matrix. InTable 6, sample 12, when a high amount of fiber was used the samplelacked consolidation and could not be tested.

As armor has progressed so has ballistic technology. Presently, armor isdesirable to protect against flechettes. Flechettes are sharpenednail-like projectiles having a sharp end and fins at the end oppositethe sharp end. They are essentially metal darts. They are metallic,about 0.15 to 1.5 inches long. It is desirable to develop compositesuseful as armor which can resist the penetration of sharp projectilessuch as flechettes.

SUMMARY OF THE INVENTION

The present invention is a method of making a composite from a fibrousweb and a matrix composition, preferably a polymeric composition. Themethod comprises the step of nonuniformly impregnating a fibrous webwith a matrix composition.

A fibrous web is a layer defined by a plurality of fibers. Typically,the layer is thin and defines a surface, with the major plane of the webcorresponding to the surface of the web. Preferably, the fibrous web isa tape or layer in which the fibers are unidirectional By unidirectionalit is meant that the fibers are parallel to each other within the web.By nonuniformly impregnating the web, it is meant that the polymericcomposition is nonuniformly distributed in the major plane of the web ina regular or random pattern.

A specific embodiment of the present invention is a method of making acomposite of a fibrous web in a polymeric matrix. The method comprisesfeeding a polymeric composition into contact with a fibrous web. Thecomposite comprises from 1 to 15, preferably 2 to 10 volume percent ofthe polymeric composition and a corresponding volume precent of thefibrous web. In the composite, the polymeric composition is nonuniformlydistributed as a matrix for the fibrous web. Alternately, the fibrousweb is nonuniformly impregnated or coated with the polymericcomposition.

In a specific and preferred embodiment of the method of the presentinvention, the step of nonuniformly distributing the polymericcomposition comprises feeding the polymeric composition with the fibrousweb to the gap between two adjacent compression rolls. At least one ofthe rolls has a patterned surface The patterned surface can compriseraised surfaces upon at least one roll. At the gap between rolls, theraised surfaces result in a narrower gap between the two adjacentcompression rolls. When the raised surfaces are located at the gap, thepolymer is forced away from the raised surfaces as the polymer andfibrous web pass through the gap. The resulting composite layer is afibrous web impregnated with a polymeric material, resulting inlocalized lower matrix content. The polymeric material is nonuniformlydistributed so that there is a patterned surface with portions of theweb having greater amounts of polymer than other portions. Theseportions are thicker areas, having greater resin content, than the areaswhich have been impressed by the raised surfaces at the narrow gap. Thethicker portions have a greater polymer to fiber ratio than areas of thecomposite which passed through the narrower gap and have a lower polymerto fiber ratio. The total amount of polymer necessary to maintain theintegrity of the polymer impregnated web is reduced. It is preferredthat the thick areas which provide the integrity of the polymeric layerare a continuous area along the surface of the fibrous/polymericcomposite.

The fibrous polymeric composite made by the process of the presentinvention maintains its integrity yet results in a composite which has agreater volume ratio of fiber to polymer, than a composite made from afibrous web in a matrix layer having a uniform thickness over the areaof the web.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an equipment layout used to illustratethe method of the present invention.

FIG. 2 is an illustration of a roll having a patterned surface which isuseful in the method of the present invention.

FIG. 3 is an illustration of a preferred fibrous web nonuniformlyembedded with a polymer composition.

FIG. 4 is a sectional view of a portion of the web in FIG. 1.

FIGS. 5-8 are schematic diagrams illustrating different shape andpattern distributions useful in the present invention.

FIG. 9 is a sectional view of an alternate embodiment of the presentinvention.

FIG. 10 is a composite made from 2 layers of the web of FIG. 3.

FIG. 11 is a sectional view of the composite of FIG. 10.

FIG. 12 is a schematic view of an equipment layout useful in the presentinvention.

FIG. 13 is a side view of a roll useful in the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be understood by those skilled in the art byreference to the accompanying Figures.

The present invention is directed to a method of nonuniformlydistributing a matrix material, preferably a polymer composition as amatrix for a fibrous web. The present invention is particularly usefulfor making composites comprising fibrous webs in a polymeric matrixwhere there is very high volume percent of fiber compared to the volumepercent of the polymer composition. Preferably there is from 2 to 15 andmore preferably 2 to 10 and most preferably 2 to 5 volume percent ofpolymer composition and a corresponding amount of fibrous web. Bynonuniformly distributing the polymer matrix, high volumes of fiber canbe incorporated and result in a structure which has improved physicalintegrity during processing and use, such as cutting the composite, andstacking unidirectional prepreg tape. By maintaining its intergrity andability to be handled, it means that the fibrous polymer compositeretains its structure without yarn separation during processing and use.More than one layer of the fibrous web impregnated with resin can bebuilt up to form a multi-layer laminate. This multilayer compositelaminate has been found to be resistant to impact, and more specificallyresistant to impact by, narrow sharp objects having an average diameterof less than 0.125 inches such as flechettes.

A specific and preferred embodiment of the present invention isillustrated in FIG. 1. This embodiment is directed to a method of makinga composite comprising a fibrous web wherein the fibers areunidirectionally oriented. However, the method of the present inventioncan be used with any fibrous web such as, knitted or woven fiber.

Fiber (10), such as yarn, is fed from bobbins (12) through a suitablemeans such as combs to align the fibers (10). Means to align the fiber(14) can be a comb, or series of pegs or rolls used to separate andalign the fibers in a desired configuration such as unidirectionallywith a given number of yarn ends per inch of web width.

The fibrous web (16) that forms is maintained by suitable constraints tocontrol the number of ends per inch of the fibers. Preferably, a carrierweb (18) is used to support the fibrous web (16). The carrier web (18)is provided from a carrier web roll (20) and directed to suitable rollsto support the fibrous web.

A polymeric composition (22) is fed from polymer composition feed means(24) onto the fibrous web supported by carrier web (18). The polymercomposition (22) fibrous (16) and carrier web (18) are pulled towardcompression rolls 26 and 28. At least one of the compression rolls is apatterned compression roll. In FIG. 1 compression roll (28) is apatterned compression roll. Compression roll (28) is shown isometricallyin FIG. 2. As the carrier web and fiber web pass through the gap betweenrolls (26) and (28) polymer composition is impregnated into the fibrousweb along the width of the rolls.

The polymeric composition is nonuniformly distributed along the width ofthe fibrous web. This is accomplished by the patterned surface on atleast one of the compression rolls. The patterns are preferably raisedareas or protrusions (30) on the surface of the roll (28). This resultsin the gap between the two compression rolls (26) and (28) varying alongthe length of the rolls. At locations where there are protrusions thegap is narrower, and at locations where there are no patterns orprotrusions the gap is wider. When the carrier web and fibrous web withthe polymer, pass through the gap between the compression rolls (26) and(28) the protruding pattern surface results in the narrower gap betweenthe adjacent rolls. This forces the polymer away from the raisedsurfaces and the polymer passes through the wider gap. This results in acomposite layer having thick layers having a greater polymer to fiberratio and areas of the composite having a lower polymer to fiber ratio.

In a preferred method the pattern compression roll (28) is in contactwith carrier web (18). This permits the pattern roll to remain clean andnot in contact with the polymer composition (22). Preferably theprotruding patterned portion is a discontinuous area while thenon-protruding patterned area, or the area which results in the widergap is a continuous area. In a preferred design the pattern is aplurality of raised or protruding areas (30). In the embodiment shown inFIGS. 1 and 2 and used to prepare the polymer impregnated webs of FIGS.3 and 4 the protrusions (30) are raised circles.

The protrusions are spaced on the patterned roll in a pattern whichpreferably is regular pattern but can be random pattern of randomshapes. The protrusions occupy from 10 to 90% and preferably 50-90% ofthe area of at least one roll. The protusions are preferably distributedin a regular distribution. In a preferred embodiment of a roll shown inFIG. 2, the patterned compression roll (28) has raised or protrusions(30). The protrusions are preferably from 0.005 to 0.10 inches high, andpreferably 0.010 to 0.050 inches high. The protrusions have an area ofat least about 0.03 square inches, preferably from about 0.5 squareinches to about 100 square inches, more preferably from about 0.5 squareinches to 20 square inches and most preferably from 0.75 square inchesto about 10 square inches. The protrusions (30) are preferbly circleshaving a diameter of 0.2 inches to 4 inches and preferably 0.3 inches to3 inches and most preferably 0.5 to 1.5 inches. The circles can be madeof circles of plastic film adhered to the roll by a suitable adhesivemeans. The protrusions can be transverse strips in the axial directionon the roll. Where a unidirectional fibric web is used, the strips canbe perpendicular to the direction of the fibers.

The gap 32 between rolls can vary depending on the thickness of thefibrous web, the amount of polymeric composition to be impregnated intothe fibrous web and the distribution and height of the protrusions (30).

The composites have a high fiber content. There is from 85 to 98 andpreferably 90 to 98 and more preferably 95 to 98 volume percent of fiberin the composite. The remainder is a matrix of a polymer composition.Each layer of the composite of the present invention has a distributionof polymer which is in a pattern wherein there are areas of thecomposite which are thick and have a greater polymer to fiber ratio andareas of the composites which are thinner areas having a lower polymerto fiber ratio. The polymer matrix to fiber ratio in a thick area ispreferably from at least 1.5 times greater, more preferably to 2 to 20and most preferably from 2 to 10 times greater than the polymer to fiberratio in thin areas.

FIGS. 3 and 4 illustrate a composite comprising impregnated fibrous web(34). The fibers (10) are unidirectionally oriented. The fibrous web iswithin a matrix of polymer composition (22). The polymer composition isnot uniformly distributed along the web. Rather, there are thin areas onthe surface of the fibrous web which have impressions resulting from theprotrusions (30). These areas generally have a shape corresponding tothe shape of the protrusion (30). There are thin sections (38) at thelocation of the impression in the web by the protusion (30) which has athickness which is thinner than the thick section (40) of the web. Thethickness of the thick section (40) at the thick areas of the web isequivalent to the thickness resulting from the gap between the rollswhere there are no protrusions. FIG. 4 illustrates a cross sectionalarea of a portion of impregnated fibrous web (34) illustrating theimpressions (36) resulting in a thinner web dimension at the location ofthe impression compared to the thicker portion of the web (40) locatedaway from the protrusions or impressions. The composite of FIG. 4 hasimpressions (36) only on one side (21). The second side (23) is flat.

The shape of the protrusion is not crtical. There should be a sufficientamount of matrix composition in the thick section (40) to providestructural integrity and increased strength compared to a composite withthe same volume percent matrix and volume percent fiber as a compositehaving a uniform thickness, with no thin section, over the area of thecomposite layer. The shape of the areas of thick section (40) areparticularly important where composite layers are made of unidirectional(parallel) fibers. The thick section (40) provide improved structuralintegrity in a direction at an angle, preferably perpendicular to thedirection of the fiber.

Alternate shapes of the protrusion (30) can be used to result in adifferent pattern of thick sections (40) and thin section (38) of thecomposite layer.

FIGS. 5 through 8 show a variety of alternate patterns useful on a layerof composite which comprises unidirection fiber in the axial direction(42).

FIG. 9 illustrates an alternate composite layer made from an embodimentwhere both compression rolls (26) and (28) have protrusion (30).Reference characters correspond to those in FIG. 4.

The fibrous web of the present invention maintains thin section (38) andthick section (40) during processing. The area of the protrusion (30)should be large enough so that the impression (38) remains after formingthe composite layer, resulting in thin section (38). It has been foundthat even when less viscous matrix compositions are used thin sections(38) remain.

In alternate embodiments of the present invention, the nonuniformdistribution of the matrix composition can be attained by other means.For example the present invention includes laminating a fibrous web withat least one continuous layer of polymeric composition and at least oneadditional layer which comprises a discontinuous polymer distribution.This could be applied by feeding polymer onto the first layer in apatterned fashion or by using a perforated layer or layer having apattern wherein there are areas without polymer and areas with polymer,i.e. holes. The layers which comprise the continuous polymeric layer andthe discontinuous polymeric layer can be laminated with a fibrous webunder heat and pressure to result in nonuniformly impregnated a fibrousweb with a matrix composition. This results in an impregnated polymerweb which could have from 2 to 15 volume percent resin distributedsufficiently to enable the web to maintain its integrity despite thehigh volume percent of fiber.

The present invention is useful to make a composite article ofmanufacture which comprises a network of high strength fibers having atensile modulus of at least about 160 g/denier and a tenacity of atleast about 7 g/denier in a suitable matrix, preferably an elastomericmatrix material. The fiber is tested according to ASTMD 2256 using 4Dtire and cord clamps, on an Instron testing machine at an elongation of100%/minute. Preferably the elastomeric composition has a tensilemodulus of less than 20,000 psi, preferably less than 6000 psi measuredaccording to ASTM D638-84 at 25° C.

For the purposes of the present invention, fiber is an elongate body thelength dimension of which is much greater than the transverse dimensionsof width and thickness. Accordingly, the term fiber includesmonofilament fiber, ribbon, strip, and the like having regular orirregular cross-section.

The fibrous web used in the method of the present invention comprisesany fibers useful to make composites. A preferred fiber networkcomprises highly oriented ultra high molecular weight polyethylenefiber, highly oriented ultra high molecular weight polypropylene fiber,aramid fiber, polyvinyl alcohol fiber, polyacrylonitrile fiber,fiberglass, ceramic fibers or combinations thereof. U.S. Pat. No.4,457,985 generally discloses such oriented ultra high molecular weightpolyethylene and polypropylene fibers, the disclosure of which is herebyincorporated by reference to the extent not inconsistent herewith. Inthe case of polyethylene, suitable fibers are those highly orientatedfibers of weight average molecular weight of at least about 500,000,preferably at least about one million and more preferably between abouttwo million and about five million. The tenacity of the fibers isordinarily at least about 15 g/denier, more preferably at least about 25g/denier and most perferably at least about 30 g/denier. Similarly, thetensile modulus of the fibers, as measured by an Instron tensile testingmachine, is ordinarily at least about 300 g/denier, preferably at leastabout 1,000 g/denier and most preferably at least about 1,500 g/denier.

In the case of polypropylene, highly oriented polypropylene fibers ofweight average molecular weight at least about 750,000, preferably atleast about One million and more preferably at least about two millionmay be used. Since polypropylene is a much less crystalline materialsthan polyethylene and contains pendant methyl groups, tenacity valuesachievable with polypropylene are generally substantially lower than thecorresponding values for polyethylene. Accordingly, a suitable tenacityis at least about 8 g/denier, with a preferred tenacity being at least11 g/denier. The tensile modulus for polypropylene is at least about 160g/denier, preferably at least about 200 g/denier. The melting point ofthe polypropylene is generally raised several degrees by the orientationprocess, such that the polypropylene fiber preferably has a main meltingpoint of at least about 168° C., more preferably at least about 170° C.

Aramid fiber is formed principally from the aromatic polyamide. Aromaticpolyamide fibers having a modulus of at least about 400 g/denier andtenacity of at least about 18 g/denier are useful for incorporation intocomposites of this invention. For Example, poly(phenylenediamineterephalamide) fibers produced commercially by Dupont Corporation underthe trade name of Kevlar 29 and 49 and having moderately high moduli andtenacity values are particularly useful in forming ballistic resistantcomposites. (Kevlar 29 has 500 g/denier and 22 g/denier and Kevlar 49has 1000 g/denier and 22 g/denier as values of modulus and tenacity,respectively).

In the case of polyvinyl alcohol (PV-OH), PV-OH fibers having a weightaverage molecular weight of at least about 100,000, preferably at least200,000, more preferably between about 5,000,000 and about 4,000,000 andmost preferably between about 1,500,000 and about 2,500,000 may beemployed in the present invention. Usable fibers should have a modulusof at least about 160 g/denier, preferably at least about 200 g/denier,more preferably at least about 300 g/denier, and a tenacity of at leastabout 7 g/denier, preferably at least about 10 g/denier and morepreferably at least about 14 g/denier and most preferably at least about17 g/denier. PV-OH fibers having a weight average molecular weight of atleast about 500,000, a tenacity of at least about 200 g/denier and amodulus of at least about 10 g/denier are particularly useful inproducing ballistic resistant composites. PV-OH fibers having suchproperties can be produced, for example, by the process disclosed inU.S. Pat. No. 4,559,267 to Kwon et al. and commonly assigned.

In the case of polyacrylonitrile (PAN), PAN fiber of molecular weight ofat least about 400,000, and preferably at least 1,000,000 may beemployed. Particularly useful PAN fiber should have a tenacity to atleast about 10 g/denier and an energy to break of at least about 22joule/g. PAN fiber having a molecular weight of at least about 400,000,a tenacity of at least about 15-20 g/denier and an energy to break of atleast about 22 joule/g is most useful in producing ballistic resistantarticles: and such fibers are disclosed, for example, in U.S. Pat. No.4,535,027.

The fibers may be arranged in networks having various configurations.For example, a plurality of fibers can be grouped together to form atwisted or untwisted yarn. The fibers or yarn may be formed as a felt,knitted or woven (plain, satin and crow feet weaves, etc.) into anetwork, fabricated into non-woven fabric, arranged in a parallel array,layered, or formed into a fabric by any of a variety of conventionaltechniques. Among these techniques, for ballistic resistanceapplications we prefer to use those variations commonly employed in thepreparation of aramid fabrics for ballistic-resistant articles. Forexample, the techniques described in U.S. Pat. No. 4,181,768 and in M.R. Silyquist et al. J. Macromel Sci. Chem., A7(1), pp. 203 et. seq.(1973) are particularly suitable.

The fibers or fabrics may be premolded by subjecting them to heat andpressure. For extended chain polyethylene fibers, molding temperaturesrange from about 20°-155° C., preferably from about 80°-145° C., morepreferably from about 100°-135°, and more preferably from about100°-130° C. The pressure may range from about 10 psi to about 10,000. Apressure between about 10 psi and about 100 psi, when combined withtemperatures below about 100° C. for a period of time less than about0.5 min., may be used simply to cause adjacent fibers to stick together.Pressures from about 100 psi to about 10,000 psi, when coupled withtemperatures in the range of about 150°-155° C. for a time of betweenabout 1-5 min., may cause the fibers to deform and to compress together(generally in a film-like shape). Pressures from 100 psi to about 10,000psi, when coupled with temperatures in the range of about 150°-155° C.for a time of between 1-5 min., may cause the film to become translucentor transparent. For polypropylene fibers, the upper limitation of thetemperature range would be about 10°-20° C. higher than for extendedchain polyethylene fiber.

The fibers premolded if desired may be precoated with a polymericmaterial preferably an elastomer which can be used to precoat the fiberprior to being arranged in a network as described above. The elastomericmaterial can also be used as the matrix has a tensile modulus, measuredat about 23° C., of less than about 20,000, preferably less than 6,000psi (41,400 kPa). Preferably, the tensile modulus of the elastomericmaterial is less than about 5,000 psi (34,500 kPa), and most preferablyis less than about 2,500 (17,250 kPa) to provide even more improvedperformance. The glass transition temperature (Tg) of the elastomer ofthe elastomeric material (as evidenced by a sudden drop in the ductilityand elasticity of the material) is preferably be less than about 0° C.Preferably, the Tg of the elastomer is less than about -40° C., and morepreferably is less than about -50° C. The elastomer should have anelongation to break of at least about 50%. Preferably, the elongation tobreak is at least about 100%, and more preferably, it is about 300% formore superior preformance.

A wide variety of elastomeric materials and formulations may be utilizedin this invention. Representative examples of suitable elastomers of theelastomeric material have their structures, properties, and formulationstogether with cross-linking procedures summarized in the Encyclopedia ofPolymer Science, Volume 5, "Elastomers-Synthetic" (John Wiley and SonsInc., 1964). For example, any of the following materials may beemployed: polybutadiene, polyisoprene, natural rubber,ethylene-propylene copolymers, ethylenepropylene-diene terpolymers,polysulfide polymers, polyurethane elastomers, chlorosulfonatedpolyethylene, polychloroprene, plasticized polyvinylchloride usingdioctyl phthalate or other plasticers well known in the art, butadieneacrylonitrile elastomers, poly(isobutylene-co-isoprene), polyacrylates,polyesters, polyethers, fluoroelastomers, silicone elastomers,thermoplastic elastomers, copolymers of ethylene.

Particularly useful elastomers are block copolymers of conjugated dienesand vinyl aromatic monomers. Butadiene and isoproprene are preferredconjugated diene elastomers. Styrene, vinyl toluene and t-butyl styreneare preferred conjugated aromatic monomers. Block copolymersincorporating polyisoprene may be hydrogenated to produce thermoplasticelastomers having saturated hydrocarbon elastomer segments. The polymersmay be simple tri-block copolymers of the type A-B-A, multi-blockcopolymers o the type (AB)n(n=2-10) or radial configuration copolymersof the type R-(BA)×(x=3-150): wherein A is a block from a polyvinylaromatic monomer and B is a block from a conjugated diene elastomer.Many of these polymers are produced commercially by the Shell ChemicalCo. and described in the bulletin "Kraton Thermoplastic Rubber",SC-68-81.

Most preferably, the elastomeric material consists essentially of one ormore of the above noted elastomers. The low modulus elastomeric materialmay also include fillers such as carbon black, silica, glassmicro-balloons, etc. up to an amount not to exceed about 300% by weightof elastomer, preferably not to exceed about 100% by weight, and may beextended with oils and vulcanized by sulfur, peroxide, metal oxide, orradiation cure systems using methods well known to rubber technologistsof ordinary skill. Blends of different elastomeric materials may be usedtogether or one or more elastomeric materials may be blended with one ormore thermoplastics. High density, low density, and linear low densitypolethylene may be cross-linked to obtain a material of appropriateproperties, either alone or as blends.

The proportion of the matrix material to the fibers or fabrics may varyfrom 1 to 50 volume percent depending upon whether the coating materialhas any impact or ballistic-resistant properties of its own (which isgenerally not the case) and upon the rigidity, shape, heat resistance,wear resistance, flammability resistance and other properties desired.In general, ballistic-resistant articles of the present inventioncontaining coated fibers should have a relatively minor proportion ofcoating 2 to 15, preferably 2 to 10 volume percent, since theballistic-resistant properties are almost entirely attributable to thefiber. The fiber network comprises at least about 85 volume percent,more preferably at least about 90 volume percent, and most preferably atleast about 95 volume percent.

The fibers can be precoated prior to being formed into the composite bythe method of the present invention. The coating may be applied to thefiber in a variety of ways. One method is to apply the resin of thecoating material to the stretched high modulus fibers either as aliquid, a sticky solid or particles in suspension, or as a fluidizedbed. Alternatively, the coating may be applied as a solution or emulsionin a suitable solvent which does not adversely affect the properties ofthe fiber at the temperature of application. While any liquid capable ofdissolving or dispersing the coating polymer may be used, preferredgroups of solvents include water, paraffin oils, ketones, alcohols,aromatic solvents or hydrocarbon solvents including paraffin oil,xylene, toluene and octane. The techniques used to dissolve or dispersethe coating polymers in the solvents will be those conventionally usedfor the coating of similar elastomeric materials on a variety ofsubstrates.

Other techniques for applying the coating to the fibers may be used,including coating of the high modulus precursor (gel fiber) before thehigh temperature stretching operations, either before or after removalof the solvent from the fiber. The fiber may then be stretched atelevated temperatures to produce the coated fibers. The gel fiber may bepassed through a solution of the appropriate coating polymer (solventmay be paraffin oil, aromatic or aliphatic solvent) under conditions toattain the desired coating. Crystallization of the high molecular weightpolyethylene in the gel fiber may or may not have taken place before thefiber passes into the cooling solution. Alternatively, the fiber may beextruded into a fluidized bed of the appropriate polymeric powder.

The fibers and networks produced therefrom are formed into compositematerials as the precursor or prepreg to preparing the compositearticles. The term, composite, is intended to mean combinations of fiberor fabric with matrix material, which may include other materials suchas fillers, lubricants or the like as noted heretofore.

A particularly effective technique for preparing a composite prepregcomprised of substantially parallel, unidirectionally aligned fibersincludes the steps of pulling a fiber through a bath containing asolution of an elastomer matrix, and helically winding this fiber into asingle sheet-like layer around and along the length of a suitable form,such as a cylinder. The solvent is then evaporated leaving a prepregsheet of fiber embedded in a matrix that can be removed from thecylindrical form. Alternatively, a plurality of fibers can besimultaneously pulled through the bath of elastomer solution and laiddown in closely positioned, substantially parallel relation to oneanother on a suitable surface. Evaporation of the solvent leaves aprepreg sheet comprised of elastomer coated fibers which aresubstantially parallel and aligned along a common fiber direction. Thesheet is suitable to nonuniformly distribute the matrix composites andsubsequently processing such as cutting, stacking and laminating toanother sheet.

Composite materials may be constructed and arranged in a variety offorms. It is convenient to characterize the geometries of suchcomposites by the geometries of the fibers and then to indicate that thematrix material may occupy part or all of the void space left by thenetwork of fibers. One such suitable arrangement is a plurality oflayers of laminates in which the coated fibers are arranged in asheet-like array and aligned parallel to one another along a commonfiber direction. Successive layers of such coated, unidirectional fiberscan be rotated with respect to the previous layer. An example of suchlaminate structures are composites with the second, third, fourth andfifth layers rotated +45°, -45°, 90° and 0°, with respect to the firstlayer, but not necessarily in that order. Other examples includecomposites with alternating layers rotated 90° with respect to eachother.

FIGS. 10 and 11 illustrate a composite made using the unidirectionalfibrous composite layers of the present invention.

One technique for forming laminates includes the steps of arrangingcoated fibers into a desired network structure, and then consolidatingand heat the overall structure to cause the coating material to flow andoccupy the remaining void spaces, thus producing a continuous matrix.Another technique is to arrange layers or other structures of coated oruncoated fiber adjacent to and between various forms, e.g. films, of thematrix material and then to consolidate and heat set the overallstructure. In the above cases, it is possible that the matrix can becaused to stick or flow without completely melting. In general, if thematrix material is only heated to a sticking point, generally morepressure is required. Also, the pressure and time to set the compositeand to achieve optimal properties will generally depend on the nature ofthe matrix material (chemical composition as well as molecular weight)and processing temperature.

The following examples are presented to provide a more completeunderstanding of the invention. The specific techniques, conditions,materials, proportions and reported data set forth to illustrate theprinciples of the invention are exemplary and should not be construed aslimiting the scope of the invention.

EXAMPLE 1

The prepreg machine used to produce the uniaxial prepreg web compositewith designed patterns is schematically shown in FIG. 12. A total of 96yarn strands, or yarn ends of Spectra 1000 extended chain polyethylenehaving a reported yarn tenacity of approximately 33 g/denier, andmodulus of approximately 1250 g/denier, an energy to break ofapproximately 55 joules/g, a yarn denier of about 650, an individualfilament denier of approximately 5.5 (118 filaments per untwisted yarn),a weight average molecular weight of about 2×10⁶, were pulled fromcreels (62) and collimated in parallel fashion by using a steel comb(64) with 1/16 inch spacing between neighboring pins. This resulted in ayarn web of 6 inch width with 16 yarn ends per inch web width. Theparallel yarn web was supported by a silicone coated paper (66) ofapproximately 0.005 inch thick. A traverse coater (68) coated thetraveling yarn web with a solution of thermoplastic Kraton D1107styrene-isoprene-styrene block copolymer (SIS) of 5% by weight anddissolved in methylene chloride of 95% by weight. The SIS is reported tohave a glass transmition temperature of -55° C. a melt index of 9 g/10min using ASTM D 1238 Condition G: and a modulus of 100 psi at 300%elongation tested according to ASTM-D462 with a jaw separation speed of10 in/min. The yarn web was pulled at a speed of 11 feet per minute. Thecoating solution was pumped by a gear pump into a tube of 0.20 inchdiameter at a flow rate of 60 grams/minute. The tube traversed acrossthe yarn web in cyclic motion of approximately 50 cycles per minute.

The yarn, coated with resin was then pulled through a pair of rollers(70) which defined the matrix coating pattern. The top roll (72) had adiameter of 6 inches and length of 16 inches. The bottom patterned roll(74) also had a diameter of 6 inches and length of 16 inches. The bottomroll had a circular patterned of circles of 3/4 inch diameter×0.005 inchthick adhered to the roll surface. The gap between the compression rollswas 0.007 inches. FIG. 13 shows the designed pattern with circularpatches, the center-to-center distance was S₁ =2 inch and S₂ =1.5 inchmeasured along axial and radial direction of the roll, respectively. Theratio of the circular patterned area to the cylindrical surface area wasapproximately 35%. After coating, the yarn web had a matrix pattern of"perforated plate" as shown in FIGS. 3 and 4 where the resin "rich" and"poor" areas corresponded to cylindrical surface covered without andwith circular patches, respectively. The overall resin content was 5%,or, the yarn content was 95%.

The yarn web coated with matrix of "perforated plate" pattern was pulledby a pair of pull rolls (80) through an oven (82) at air temperature of95° C. where the solvent was eliminated. Afterwards, the uniaxialprepreg tape was wound on a rewinder (84). The uniaxial prepreg webaverage thickness was measured to be approximately 0.002 inch thick.

EXAMPLE 2

A prepreg made according to the process of Example 1 has been examinedto determine the variation of matrix content along the length of theprepreg (along reinforcing fiber direction) in a central portion of theprepreg, using infrared spectrometry. A rectangular aperture 10 mm by 7mm was used with the 7 mm dimension being parallel to the fiberdirection of the sample which allows a spacial sampling of center ±3.5mm. The data was generated using a PERKIN ELMER 983 ratio recording dualbeam dispersive infrared spectrophotometer. The region scanned was from100 cm⁻¹ to 601 cm⁻¹ at a 3 cm⁻¹ resolution at 1000 cm⁻¹ condition. Theanalytical absorbances used were the 700 cm⁻¹ assigned to polyethyleneand the 700 cm⁻¹ assigned to polystyrene. The absorbance ratio 700 cm⁻¹/720 cm⁻¹ was calculated and is proportional to the ratio of the matrixto fiber in the prepreg. The variation of this ratio is shown as afunction of distance along a central portion of the prepreg length inTable 1, and clearly demonstrates that matrix concentration variesregularly down the prepreg length, with the maximum concentration beingapproximately three times that of the minimum.

                  TABLE 1                                                         ______________________________________                                        VARIATION OF ABSORBANCE RATIO                                                 ALONG PREPREG LENGTH                                                          CENTER OF SCANNING                                                            LOCATION                                                                      (mm)              ABSORBANCE RATIO                                            ______________________________________                                         25               0.18                                                         50               0.184                                                        75               0.14                                                        100               0.06                                                        125               0.13                                                        150               0.07                                                        175               0.146                                                       200               0.117                                                       225               0.08                                                        250               0.14                                                        275               0.16                                                        300               0.16                                                        325               0.195                                                       350               0.107                                                       375               0.144                                                       400               0.16                                                        425               0.146                                                       450               0.184                                                       475               0.116                                                       500               0.11                                                        525               0.224                                                       550               0.05                                                        ______________________________________                                    

EXAMPLE 3

The prepreg layers of the type made in Example 1 were cut square andstacked with fiber direction perpendicular to the fiber direction of theprevious layer. The stacked prepregs were placed between Apollo plates(0.05 cm thick chrome coated steel plates (0.05 cm thick chrome coatedsteel plates) and molded for 30 minutes in a hydraulic press havingplaten temperatures of 130° C. and pressure of 5.5 mPa. (800 psi).Composites were cooled in the press under pressure. Ballistic testing(Mil-Spec MIL-P-46593A(ORD)) was carried out against steel flechettesweighing 1.34 g, with pointed tip and trailing fins, 2.6 mm shaftdiameter and an overall length of 35 mm. Results of ballistic testingagainst the steel flechettes are given in Table 2 and demonstrate thatthe composite constructed from patterned prepregs having 95 wt % fibercontent. Comparison was made to prepregs having the indicated fibercontent of 84 weight percent in Samples 2 and 3, and 69 weight percentin Sample 4. The fiber type and matrix composition were the same as inExample 1.

Usually, a composite armor has the geometrical shape of a shell orplate. The specific weight of the shells and plates can be expressed interms of the areal density corresponds to the weight per unit area ofthe strucutre. In the case of fiber reinforced composites, the ballisticresistance of which depends mostly on the fiber, another useful weightcharacteristic is the fiber areal density of composites. This termcorresponds to the weight of the fiber reinforcement per unit area ofthe composite.

In Table 2 "ad" is the fiber areal density which is the weight per areaof a single prepreg layer: and "adt" is the total areal density of thetotal prepreg weight per area including the resin. AD and ADT are thecorresponding values for a multi layer composite. Areal density andtotal areal density are reported as kg/m².

The protective power of a structure is normally expressed by citing theimpacting velocity at which 50% of the projectiles are stopped, and isdesignated the V₅₀ value.

To compare structures having different V₅₀ values and different arealdensities, the following examples state the ratios of (a) the kineticenergy (Joules) of the projectile at the V₅₀ velocity, to (b) the arealdensity of the fiber or of the composite (kg/m²). These ratios aredesignated as the Specific Energy Absorption (SEA) and Specific EnergyAbsorption of Composite (SEAC), respectively.

                                      TABLE 2                                     __________________________________________________________________________    BALLISTIC PERFORMANCE OF BALLISTIC COMPOSITES                                 AGAINST FLECHETTES                                                            Sample    Prepreg Target  V50                                                 No.  Type ad  adt AD  ADT (ft./S)                                                                           SEA                                                                              SEAC                                         __________________________________________________________________________    (A) 95 wt % Fiber                                                             1    Pattern                                                                            0.04517                                                                           0.04755                                                                           6.68                                                                              7.0 1248                                                                              14.5                                                                             13.9                                         (B) 84 wt % Fiber                                                             2    Standard                                                                           0.03507                                                                           0.04175                                                                           4.21                                                                              5.01                                                                              655 6.35                                                                             5.34                                         3    Standard                                                                           0.03507                                                                           0.04175                                                                           7.56                                                                              9.0 833 5.27                                                                             4.80                                         (C) 69 wt % Fiber                                                             4    Standard                                                                           0.0431                                                                            0.06241                                                                           6.37                                                                              9.25                                                                              853 7.12                                                                             4.90                                         __________________________________________________________________________     All areal densities are reported in the usual units of kg/m.sup.2             Sea and seat are in units of J · m.sup.2 /kg                    

COMPARATIVE EXAMPLE 1

Example 1 was repeated with the exception that the circular patches weretaken off from the roll surface and the gap between the compressionrolls were reduced to 0.006 inch approximately in order to produce resincoated yarn web of approximately 95% yarn content. The resin coated yarnweb was extremely difficult to handle and yarn separation was observedduring cutting and stacking into multi laminated layers.

What is claimed is:
 1. A method of making a composite of aunidirectional fibrous web in a polymer matrix composition comprisingthe steps of:nonuniformly feeding a polymer composition into contactwith a unidirectional fibrous web into a gap between two adjacentcompression surfaces with at least one of the surfaces having a pattern,whereby the polymer composition is nonuniformly distributed into thickareas and thin areas as a matrix for the fibrous web in a ration of from2 to 15 volume percent of the polymer composition and corresponding85-98 volume percent of the fiber.
 2. The method as recited in claim 1wherein there is from 2 to 10 volume percent of the polymercompositions.
 3. The method as recited in claim 2 wherein there is from2 to 5 percent of the polymer compositions.
 4. The method as recited inclaim 1 wherein the patterned surface comprises a plurality ofprotrusions upon at least one roll, the protrusions resulting in anarrower gap between the two adjacent rollers at the location of theprotrusions which are located at the gap.
 5. The method as recited inclaim 1 wherein the composite comprises the thick sections over acontinuous area of the web.
 6. The method as recited in claim 1 whereinthe composite comprises the thin sections over a discontinuous area ofthe web.
 7. The method as recited in claim 1 wherein the two adjacentcompression surfaces comprise rolls, both of which have a patternedsurface.
 8. The method as recited in claim 1 wherein the matrixcomposition is distributed so that the ratio of polymer to fiber in thethick areas is at least 1.5 times greater than the ratio of polymer tofiber in the thin areas.
 9. The method as recited in claim 4 wherein theprotrusions comprise from 10 to 90 percent of the area of at least oneroll.
 10. The method as recited in claim 9 wherein the protrusionscomprise 50 to 90 percent of the area of at least one roll.